Role of CBNAAT in Extrapulmonary Tuberculosis- An ongoing pilot study

Abstract

There is a paucity of data from clinical trials in extrapulmonary tuberculosis(EPTB) and most of the information regarding diagnosis and management is extrapolated from pulmonary TB. The Xpert MTB/RIF assay or Cartridge Based Nucleic Acid Amplification Test(CBNAAT) is a semi-automated, molecular assay, which permits rapid TB diagnosis through detection of the DNA of Mycobacterium tuberculosis. We through our study wanted to highlight the role of CBNAAT in the rapid diagnosis of EPTB. We admitted all cases with suspected EPTB during the period September,2017 to December,2018. Specific samples were collected from the patients and were forwarded to Regional Medical Research Centre (ICMR) through cold chain where they were processed and taken up for CBNAAT and culture in Lowenstein-Jensen(L-J) media. Appropriate samples were sent to our RNTCP laboratory for AFB smear examination. We compared the accuracy of CBNAAT in relation to clinical diagnosis, AFB smear and L-J culture. We examined 191 samples during the period. Pleural fluid was the most common sample(30.9%) collected followed by lymph node aspirate(24.6%). The overall sensitivity and specificity of CBNAAT was determined to be 26.77%(95% CI 19.31%-35.35%) and 100%(95% CI 94.40%-100%). The low sensitivity could be due to the low sample size and majority of the sample being pleural fluid. The sensitivity and specificity of CBNAAT in relation to mycobacterial culture, however, was 76.47%(95% CI 50.1%-93.19%) and 87.93%(95% CI 82.14%-92.37%) respectively. The sensitivity and specificity of CBNAAT was at par in comparison to mycobacterial culture. However, both were highest for lymph node aspirate and pus samples and may be recommended in initial diagnosis in these cases.